The invention further relates to a method for assembling an image pick-up module, wherein an electronic image sensor is electrically bonded to a single-piece circuit board and the circuit board is electrically bonded to at least one cable leading away from the circuit board.
An image pick-up module of the before-mentioned kind is known from U.S. Pat. No. 5,220,198.
Electronic image pick-up modules of this kind find general application in the field of video recording. In addition to the use in video cameras, such electronic image pick-up modules have recently been employed in maximally miniaturized applications, especially in endoscopes for technical or medical purposes. Such endoscopes, or video endoscopes, have been disclosed, for example, in U.S. Pat. No. 5,754,313 and U.S. Pat. No. 5,166,787.
An image pick-up module comprises, generally, an electronic image sensor or image pick-up, by which light imaged on it is converted into an electric signal. Such electronic image sensors are generally implemented in CCD or CMOS technology. Further, the image pick-up module comprises at least one circuit board which accommodates the signal electronics, or at least part of the signal electronics, for the image sensor. The signal electronics comprise circuits that are implemented on the circuit board by electronic components or in the form of printed circuits. In addition, the image pick-up module comprises at least one cable, leading away from the circuit board, which is connected, at a point remote from the image pick-up module, to an electronic control and signal processing system for processing the electric signals received from the image pick-up module to reproduce the image received by the image sensor on an image reproduction unit, such as a display or a monitor.
As a rule, however, the circuit board is bonded not only to a single cable but to a system of several, partially coaxial, cables which form the electric signal transmission system between the image pick-up module and the electronic control and signal processing system.
It is only due to the miniaturization of the image sensors and the progress achieved in microtechnology that the use of such image pick-up modules in endoscopes has become possible. The image pick-up module is arranged in an endoscope in the distal tip of the endoscope shaft, i.e. the tip facing the patient, as is described in the before-mentioned U.S. Pat. No. 5,166,787. The image pick-up module replaces in this case the optical image transmission system used in “classical” endoscopes, which consist of a plurality of lenses arranged in series. Instead of transmitting the distally received image to the proximal end, i.e. the end remote from the patient, by means of an optical imaging lens system, an image pick-up module converts the optical light signals to electric signals and transmits them to the proximal end, via at least one cable or, as a rule, a cable system. The use of electronic image pick-up modules instead of optically transmitting lens systems provides the advantage, according to the before-mentioned US Patent Specification, that the image pick-up module need not be installed rigidly in the distal tip of the endoscope shaft, but can be mounted movably in that tip so that once the endoscope has been introduced into the cavity to be inspected, the image pick-up module can be pushed out distally from the shaft or can be swung out laterally from the shaft, with the effect that on the one hand a larger area can be viewed through the movable image sensor while on the other hand the endoscope shaft is released so that instruments can be introduced through the shaft into the cavity, for example. In addition, a telescope-like extension of the endoscope is also imaginable.
It is always a requirement with endoscopes that the cross-section of the outer contour of the shaft be as small as possible. Accordingly, in order to be accommodated in such a shaft, the image pick-up modules used must have the smallest possible outer cross-section. The shaft diameter of a video endoscope for medical purposes, for example, is as small as a few millimeters (<10 mm). This means that the dimensions of the miniaturized image pick-up modules should be as small as ever possible (if possible #6 mm). While presently existing image sensors, designed in so-called “case-less” configuration and with flexible connecting fingers, succeed increasingly in meeting these demands, the problem of making the overall structure of the image pick-up modules as small as possible continues to exist.
The image pick-up module known from U.S. Pat. No. 5,754,313 comprises two separate, i.e. not a single-piece, circuit boards for bonding the image sensor, which two circuit boards accommodate, in customary fashion, electronic miniature components and serve for bonding the cable system. The circuit boards extend in parallel one to the other and substantially at a right angle relative to the image pick-up surface of the image sensor. Since the signal electronics accommodated on the two circuit boards cannot function independently, an electric connection, for example in the form of lines, or a connecting circuit board must be additionally integrated which constitutes a further increase of the assembly effort connected with the image pick-up module. In addition, bonding the cables and the electric components between the boards has been found to present a problem. Further, the cables leading away from the circuit board are bonded to the circuit board on an outer surface of the latter in the case of this image pick-up module. Given the diameter of the different cables, which in part may be coaxial lines in which case they exhibit a corresponding thickness, the described structure of the known image pick-up module results in a cross-sectional diameter greater than the cross-sectional diameter defined by the image sensor.
Another problem presenting itself when such image pick-up modules are used in video endoscopes consists in that the one or the several cables, that lead away from the circuit board, may be exposed to tensile strain, especially in the case of flexible video endoscopes or when a deflection mechanism is provided for moving the image pick-up module, as described in U.S. Pat. No. 5,166,787, or during installation of the module in the endoscope shaft. Here again, the image pick-up module known from U.S. Pat. No. 5,754,313 has been found to be disadvantageous insofar as the strain relief device would have to be provided either around the bonding area of the cables on the two circuit boards, which would further disadvantageously increase the cross-sectional diameter of that known image pick-up module, or else would have to be provided at the proximal end of the circuit boards with the result that the length of the image pick-up module would be additionally increased in an undesirable way, which is a problem especially with flexible endoscopes where the stiff distal jaw parts should be kept as short as possible.
The image pick-up module known from the before-mentioned U.S. Pat. No. 5,220,198, from which the present invention starts, comprises a single-piece circuit board having three sections forming in this case the shape of a U; the present invention is, however, not restricted to that embodiment. The two sections, that are bonded to the image sensor, extend one parallel to other, the image sensor being fastened on the third section which extends crosswise to the two other sections. Accordingly, the circuit board is open on the side opposite the image sensor. This image pick-up module also provides the disadvantage that no strain relief is provided for the cables leading away from the circuit board. Under tensile strain conditions, there is therefore a risk for the cables leading away from the circuit board that the one or the several cables may be torn off the circuit board under strain.
Now, it is an object of the present invention to improve an image pick-up module of the before-mentioned kind in such a way that strain relief is provided, with small constructional effort, for the at least one cable leading away from the circuit board, without the structural dimensions of the image pick-up module being increased due to that strain relief.